1. Field of the Invention
This invention relates to a pressure switch, and more particularly to a pressure switch wherein the interior of a casing is divided by a partition into a fluid chamber fed with a fluid the pressure of which is to be detected, and a working chamber in which a switch mechanism is housed. A rod extends slidably through the partition, provided at its one end with a pressure-receiving portion which is adapted to receive a fluid pressure in the fluid chamber, and projecting at the other end portion thereof into the working chamber so as to change the switching mode of the switch mechanism in accordance with the displacement, which occurs due to a fluid pressure applied to the pressure-receiving portion, of the rod to the end thereof which is on the side of the switch mechanism. Spring means urge the rod to the side of the fluid chamber.
2. Description of the Prior Art
There is a conventional pressure switch of this kind, which consists of a fluid chamber, a metal diaphragm supported at its peripheral portion on side walls of the fluid chamber, a rod fixed at its one end to the metal diaphragm, and a switching mechanism the switching mode of which is changed when a fluid pressure is applied to the diaphragm bending the diaphragm against the resilient force thereof and thereby displacing the rod axially toward the other end thereof. In such a pressure switch, a skilled hand is required to set the resilient force to a suitable level. Therefore, it is necessary to improve the manufacturing accuracy of the diaphragm. There is also a conventional pressure switch in which a rod is urged by a coil spring. In this pressure switch, it is also troublesome to set the resilient force of the coil spring to a suitable level.
In such a pressure switch, it is necessary that the peripheral portion of the diaphragm be reliably fused to the casing for the purpose of sealing a fluid chamber and a working chamber from each other. Accordingly, special welding techniques are required. There is also a conventional pressure switch made with a view to meeting these requirements, in which a fluid pressure is applied directly to a pressure-receiving portion at one end thereof. In this pressure switch, a seal member is inserted between the rod and the partition so as to seal a fluid chamber and a working chamber from each other. Consequently, the sliding resistance of the rod increases to cause hysteresis to occur. This hampers the manufacturing of a high-pressure small-sized pressure switch having excellent performance.